1. Field of the Invention
The present invention is generally related to hard disk drives and disk drive electronic control systems. In particular, the present invention relates to a system for tangential skew correction of the transducers for reading and writing data from the disk in a disk drive system having two actuators.
2. Description of the Related Art
A disk drive system having two actuators is shown in FIG. 1 and is comprised of disk assembly 7 and actuators 8 and 9. Transducer 14 on actuator 8 and transducer 13 on actuator 9 read and write information to and from the disk on disk assembly 7. Further it is desirable for each of the transducers 13 and 14 to read data regardless which of the transducers recorded the data.
FIG. 2 shows in more detail the disk drive system having two actuators of FIG. 1. Actuator 8 has a head arm assembly 15 where each arm of the head arm assembly 15 carries a transducer to communicate with one of the surfaces of a disk in disk assembly 7. The head arm assembly 15 is connected to a motor 11 for placing a given transducer over a desired track on one of the disk surfaces of disk assembly 7. Disk assembly 7 is comprised of a plurality of disks 10, 16 and 18, shaft 19 and a motor 20. Actuator 8 employs transducers 14 and 22 to interact with top and bottom surfaces of disk 10 respectively, transducers 24 and 26 to interact with the top and bottom surfaces of disk 16 respectively and transducers 28 and 30 to interact with the top and bottom of disk 18 respectively. Actuator 9 is comprised of a motor 12, a head arm assembly 17 and transducers 13, 23, 25, 27, 29 and 31.
In a disk drive system having two actuators, one of the actuators is used as a packwriter to record on each disk surface system operational information such as servo data, sector marks, address marks and like information. Actuator 8 is used as the packwriter to record the system information on the surfaces of disks 10, 16 and 18. Thus there is no radial or tangential skew problem associated with transducers 14, 22, 24, 26, 28 and 30 because their physical location with respect to each other and with respect to the disk surface remains a constant.
The spatial relationship between transducers 14, 22, 24, 26, 28 and 30 of actuator 8 will be different than the spatial relationships between actuators 13, 23, 25, 27, 29 and 31 of actuator 9. There is no physical means to align the transducers on the head arm assembly of actuator 9 to accurately duplicate the spatial relationship of the transducers on actuator 8. The radial and tangential skew between the transducers on the head arm assemble of the nonpackwriter actuator does cause a delay in obtaining proper transducer placement over a desired track during a transducer switching operation between transducers associated with the nonpackwriter actuator.
Assuming that transducer 13 is used as the reference transducer, it can be seen from FIG. 3 that transducers 23, 25, 27, 29 and 31 can be radially offset either to the right or left of reference transducer 13. Such an offset to the right or left of transducers 23, 25, 27, 29 and 31 may cause these transducers to be located over different tracks than the reference transducer 13. Of course, a transducer may in fact be in alignment with the reference transducer 13 as shown with respect to transducer 31. Therefore, transducer 31 will be over the same track as transducer 13 which still may not be the correct track because the spatial relationship between transducers 13 and 31 may be different than the spatial relationship between packwriter transducers 14 and 30. Thus a track correction may have to be made for transducers 23, 25, 27, 29 and 31 to place the transducer over the correct track before data may be read or written properly.
FIG. 4 uses transducer 13 as a reference and shows that transducers 23, 25, 27, 29 and 31 may be tangentially offset to the front or to the rear of reference transducer 13. Where the transducer is offset to the front of reference transducer 13, the address mark will appear earlier than the address mark at the reference transducer 13. Where the transducer is set to the rear of reference transducer 13, the address mark will occur later than the address mark at the reference transducer 13.
In the disk drive system using a sectored embedded servo, control circuitry is synchronized to data read from the desired track on the disk surface. The system expects the occurrence of servo data, sector marks and address marks to occur at specific times and sets timers to trigger circuitry to search for the occurrence of servo data, sector marks and address marks.
If reference transducer 13 is being used and the system switches to transducer 23, the system would still expect the address mark to occur at the time that the address mark would have occurred for transducer 13. Therefore the start of the address mark search by the system can begin after the address mark has passed beneath transducer 23 since transducer 23 is physical ahead of transducer 13. The address mark will therefore be missed and the system would have to go through the entire synchronization procedure before the system could ascertain the track location of transducer 23.